NSF Award
2308183
Due to the complex geodynamic history of Earth, its mantle has evolved to be compositionally heterogeneous, containing several distinct components which together comprise the "geochemical mantle zoo". For example, over geologic time, Earth’s oceanic crust recycles into the mantle, introducing compositions that differ from other mantle components. To identify recycled components and their role in mantle melting that produces most of Earth’s crust today, nitrogen (N) and noble gas (He, Ne, Ar, Kr, Xe) isotopes will be measured in a suite of well-characterized oceanic lavas from seamounts near the East Pacific Rise (EPR). This multi-isotope approach will discriminate between recycled and deeply sourced mantle components in the EPR mantle. The proposed work will be completed at Woods Hole Oceanographic Institution (WHOI), using The Barry Lab, the only USA-based lab measuring these gases in extremely low concentration samples. Very few seamounts have been examined through the lens of N and noble gas isotopes, so this study will uniquely assess the nature of recycled and deep mantle volatile components, and the extent to which they are incorporated into the Pacific mantle. To increase participation in science and improve the accessibility of samples and geochemical data from WHOI’s world-class repository, PI Anderson will curate and collate existing and newly-acquired ocean basalt samples and their respective geochemical data into a map-based, user-friendly website. The website will broaden access to WHOI’s repository for future scientific research, and will provide a new accessible resource for sharing ocean science results in an interactive way that can be incorporated into public and educational outreach curriculum.<br/><br/>Ocean island and mid-ocean ridge lavas provide important clues about how Earth’s interior has evolved compositional heterogeneities over time. The influence of planet-scale processes like accretion, differentiation, convection, development of a crust, and subduction recycling can be constrained using oceanic lavas from mid-ocean ridges (MOR) and ocean islands. Most of Earth’s oceanic crust forms at mid-ocean ridges (i.e., the EPR), where mantle melts undergo less differentiation, alteration, and interaction with thick or geochemically altered crust (unlike melts forming beneath continents). Isotopic characterization of mantle-derived lavas erupted at mid-ocean ridges (MORs) can therefore reveal important information about the evolution of Earth’s mantle over time. However, MOR can dilute mantle end members due to efficient mixing of melts beneath the ridge. By contrast, seamounts forming away from the ridge by-pass this homogenization and thus better preserve end-member compositions. Therefore, to constrain mantle heterogeneity beneath the East Pacific Rise, near-EPR seamount lavas will be the focus of N and noble gas mantle heterogeneity in this study. Mantle-derived oceanic basalt glasses preserve time-integrated volatile characteristics of their source reservoir. Nitrogen and noble gas (He, Ne, Ar, Kr, Xe) isotopes vary systematically between mantle, crustal, and atmosphere reservoirs, making them powerful tools for tracing interactions between Earth’s surface and interior. Specifically, N and heavy noble gases (Ar, Kr, Xe) are potentially sensitive tracers of subduction, because they are readily incorporated into subducting slab materials (i.e., sediments, altered oceanic crust, pore water in the slab), whereas He and Ne are not recycled and are thus excellent tracers of primordial deep mantle contributions. Together, these isotope systems will be used to constrain the origin of volatiles in the Pacific mantle near the EPR. The prevalence of subducted materials and/or deeply sourced mantle components in the Pacific mantle may significantly impact upper mantle systematics like temperature and melting, and may lend insight into global volcanic activity away from plate boundaries.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
